Alcohol enhancement of hepatitis C viral (HCV) liver injury is now well recognized. Substantial evidence suggests that oxidative stress plays an important role in the severity and progression of the HCV-induced injury. The hepatic cytochromes P450, responsible for oxidative metabolism of endogenous and exogenous substrates, undoubtedly play an important role in determining the amount of hepatic oxidative stress. Since ethanol induces several P450 isoforms, including the classical ethanol-inducible CYP2El, as well as the most abundant human hepatic P450, CYP3A4, it is possible that alcohol's enhancement of HCV injury is mediated by the increased activities of these P450s. CYPs 2EI, 3A4, as well as 1A2 are known to "leak" reactive oxygen species. That HCV itself might cause oxidative stress is demonstrated by its association with acquired porphyria cutanea tarda (PCT), a model disorder of hepatic oxidative stress which is often seen in alcoholic patients. Interferon-alpha, widely used as therapy for HCV, is known to down-regulate P450s which might explain part of its beneficial effects. These findings suggest that hepatic P450s might modulate injury from oxidative stress in HCV-infected individuals and that alcohol enhancement of injury is mediated by increased P450 activities. The objective of this proposal is to investigate the hypothesis that increased activities of specific P450 isoforms induced by ethanol contribute to hepatic injury via an oxidative mechanism in HCV infected patients. Patients with mild, moderate, and severe histologic activity and matched controls will be studied utilizing the resources of the General Clinical Research Centers at the Univ. of Ky. and the Univ. Texas Medical Branch, Galveston. P450 activities will be determined using the drug probes chlorzoxazone for CYP2EI and midazolam for CYP3A4. Theophylline will be used for CYP1A2. Assessments of oxidative stress (urinary F2-isoprostanes, monocyte NFKB) and active fibrinogenesis (TGFbeta-1, N-terminal procollagen peptide III) will be correlated with P450 profiles. PCT patients will be studied before and after de-ironing therapy. Patients treated with pegylated interferon will be studied during therapy and success of therapy will be correlated with changes in P450 profiles and oxidative stress. To determine the mechanisms by which alcohol worsen's HCV injury, HCV patients with normal or only mild histologic injury and matched controls will be administered 40g ethanol/d for 10 days in the GCRC with P450 profiles determined at 0, 5 and 10 days. Daily blood ethanol, oxidative stress, transaminases, and fibrinogenesis will be assessed and changes correlated with changes in P450s. These studies will define the role of P450s in the alcohol enhancement of HCV liver injury and might suggest P450 inhibitors as therapies for HCV infected individuals even if they continue to drink alcohol.